A paper speaker's cone movement

Discussion in 'Amps and Cabs [BG]' started by capcom, Apr 21, 2005.

  1. capcom


    Mar 23, 2005
    (first of all sorry for my bad english)
    (i searched both TB and web for this subject but couldnt find an answer)

    does anybody know if the movement of outside of a paper cone is "exactly" same as the movement of its center ?

    i thought that maybe at high volumes while the center perfectly obeys the signal coming from amplifier but the outer parts may not be the same like the center of it, because it is made of paper and it can "bend" somehow ?

    and if so: is it the result of a large diameter speaker's (like 18, 15 inches) sound to be more muddy when compared to smaller ones like 12 and 10 inch speakers ?

    also: is the design philosophy of aluminum cones are perfect moving cones that does not bend so the outer and the center moves exactly the same to give a more detailed sound ?

  2. Petebass


    Dec 22, 2002
    QLD Australia
    Speaker cones do flex a little. Some have accordian like ridges throughout the cone surface to allow the flexing to occur without putting too much pressure on the cone. From memory, Hartke's aluminium cones have this feature. I know my Beyma 112nd/w does but the 12LW30/ND doesn't, so it varies from speaker to speaker.

    But for practical purposes, measuring movement at the cone centre and at the cone edge would mot likely yield different results. It certainly appears that way to my naked eye. I'm not 100% sure about this anyone else care to chime in.
  3. Basshole

    Basshole Banned

    Jan 28, 2005
    I do...and I can tell you that it most assuredly is not.

    Think about it. The speaker cone has to flex quite a bit, or else it would only be able to reproduce one frequency at a time. It wouldn't even be able to reproduce harmonic components of a single note of music if it didn't flex, it would only make the fundamental.
  4. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    The answer is: No. At higher frequencies, the outer portions of the cone vibrate less. Thus a stiffer cone will have flatter frequency response. Speakers are fairly linear, so the cone motion at high power is roughly the same as at low power, but at a higher amplitude.

    My hypothesis about why 15's and 18's are more boomy because they can be designed into big ported boxes with extended low frequency response, without sacrificing sensitivity. You can design a tight-sounding cab with a 15, but there does not seem to be much of a market for it.

    I just built a speaker with an Eminence 151311 (15", 300W, sold by Madisound) in a very small closed box, and there is no mud, boom, farting, or any other unpleasantness.
  5. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Drivers by definition are pistonic devices, so technically when all is well the entire cone will move in unison. There have been cones with separate sections for independant movement, most notably the Altec Bi-Flex, but the concept didn't exactly take the world by storm. Most drivers have low mass dust covers that act almost like tweeters in that they don't damp out high frequencies like the high mass cone does, and an extension of that concept is the whizzer. Finally there is the matter of cone break-up mode, where the cone doesn't move in unison and there are resulting spikes in the high-frequency response. In hi-fi use breakup mode is tamed by crossing the driver over well below the breakup frequency, but in MI use it's often breakup mode that is employed to extend the frequency range of the driver. The response is anything but flat, but for MI use that is what leads to the characteristic voicing of many drivers.
  6. Commercial MI cabs are boomy by design.

    Too small:
    Produces a boom in the mid bass, steep rolloff, gutless bottom.

    Just right:
    No boom, gradual rolloff, tight bottom

    Too big:
    No boom, extended bass, sloppy bottom

    Most cab manufacturers stuff acoustically large drivers into a too-small cabinet. This causes a big hump in the mid-bass (Eden XLT, Carvin) which gives the appearance of "big" bass. The audio folks do the same thing with sealed boxes... a high Q box with a hump in the mid-bass sounds "bigger" than a lower Q box. The measured result is less bass and worse transient response, but the boom appeals to the unwashed. For example, the 10" Eminence BP102 requires 2.2 to 4.0 cubic feet, each, for proper volume. This is a whole lot larger than the typical 4x10 cab.

    The "just right" alignments are SBB4, QB3, and Flat. These require more cabinet volume than commercial cabs, even those with 10" drivers. A good 12" example is the Eminence Omega Pro 12 in 1.23 cubic feet at 39 Hz. This combination has a very tight bottom and no boom. For 15", the Eminence CB15 in 3.74 cubic feet at 34 Hz is a good bet. The 15" Delta 15a favored by many commercial cab makers requires 11.5 to 28 cubic feet internal volume for correct tuning. It provides full bass all the way down without loss of sensitivity. And requires a crane to move it around...

    The "too big" is the EBS alignment (extended bass shelf) which is favored by the Avatar 4x10. This is a cab volume at 150% or larger than ideal. It extends bass response at the expense of creating muddy, large group delay. This is Delta 10a used in the Avatar cabs. This driver only requires 0.52 cubic feet, but tunes at 66 Hz in SBB4. Avatar puts 4 of these into a one-size-fits-all cabinet that is larger than required for this driver.
  7. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    You're correct that a speaker cone does not exactly move in unison, but the reason you give is not.

    An ideal cone would move all in unison. In fact, the perfect loudspeaker cone would have infinite rigidity or stiffness and zero mass. But those qualityies are impossible and in fact contradictory. So any speaker cone, or even any speaker system, is an arrangement of compromises.
  8. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Not necessarily. The ideal cone would probably have the vibrating portion change with frequency so as to maintain the same directivity. That changes with the size of the "piston" vs the wavelength.

    Since the mass of the cone restricts motion at higher frequencies (with constant drive force) you would NOT want to have to move the whole cone, unless it were massless... which would pose a design problem.

    Some of the very flattest and nicest speaker drivers I have worked with (which are 15", btw), have a ribbed cone and are designed to "decouple" the voice coil from the outer part of the cone at higher frequencies. These 15" speakers are almost flat to 5K.
  9. capcom


    Mar 23, 2005
    Thank you all for your answers.